Plug-in type power take-off device with bimetallic contacts



Jan. 12, 1960 E. A. ERICSON 2,921,146

PLUG-IN TYPE POWER TAKE-OFF DEVICE WITH BIMETALLIC CONTACTS Filed Dec. 2, 1957 2 Sheets-Sheet 1 A INVENTOR. ERIC A. ERICSON ATTORNEY Jan. 12, 1960 E. A. ERICSON 2,9

PLUG-IN TYPE POWER TAKE-OFF DEVICE WITH BIMETALLIC CONTACTS Filed Dec. 2. 1957 2 Sheets-Shet 2 INSULATION \H I FI6.7 I3 13 IN VEN TOR.

ERlc AERICSON BY RMQ Q ATTORNE Y United States Patent PLUG-IN TYPE POWER TAKE-OFF DEVICE WITH BIMETALLIC CONTACTS Eric A. Ericson, Plainville, Conn., assignor to General Electric Company, a corporation of New York Application December 2, 1957, Serial No. 700,038

4 Claims. (Cl. 191-45) My invention relates to electric power take-off devices and more particularly to electric power take-off devices of the plug-in type such as are adapted to be used with bus bar type distribution systems or busways, and including stationary take-off devices and movable or trolley type take-off devices.

In order to secure good electrical contact and to avoid heating, excessive voltage-drop, etc., in such power takeoff devices, it is necessary that adequate pressure of-the contacts upon the bus bars be provided. In general, such pressure should be proportional to the amount of current being drawn. Thus, when larger currents are to be drawn, the pressure should be of greater magnitude than when only smaller currents are involved. Very great pressure, however, makes it very diflicult to insert and remove such plug-in devices, and, in trolley type devices, tends to increase contact wear as the trolley is moved along the duct from one position to another.

Accordingly, it is an object of this invention to provide an improved power take-01f device which provides high contact pressure when needed without causing difficulty in inserting or removing such device. It is another object of the invention to provide an improved trolley type take-off device in which high contact pressure is provided only when needed, thus reducing friction and wear during ordinary movement of the device.

In accordance with the invention, there is provided an electric power take-off device including a main supporting body and a contact movable relative thereto for engagement with a busway conductor. A current responsive member is provided on the main support, connected electrically in series with the contact and adapted to exert supplementary force on the contact in a contact making direction in response to current flow therethrough. Since the magnitude of such force depends upon current flow, it is reduced in the absence of such current. This permits ready insertion or removal of the device on a busway. The invention is especially adapted for trolley type power take-off devices, where it minimizes friction and wear of contacts by providing high contact pressure only at times when it is needed. While this is of value in any application "of a trolley type device, it is especially useful in those frequent applications where power is drawn only when the device is stationary.

The invention will be more clearly understood from the following detailed description, reference being had to the accompanying drawing, and the features of novelty will be particularly pointed out in the appended claims.

Figure 1 is a perspective View of an electric power take-off device of the trolley type incorporating the invention;

Figure 2 is a perspective view of the contact supporting structure of the collector of Figure 1, with a portion of the insulating body thereof and one contact assembly removed; Figured is a plan view of a portion of the collector of Figure 1 shown in operative relation with associated ice bus bars of a busway system, a portion of the insulating body being omitted to show the contact arrangement;

Figure 4 is an exploded perspective view of a contact assembly of the collector of Figure 3;

Figure 5 is a plan view in section of a stationary power tape-ofi device embodying the invention;

Figure 6 is an exploded perspective view of the contact assembly of the collector of Figure 5;

Figure 7 is an elevation view, partly in section, of the trolley type power collector of Figure 1 in place on a power distribution duct or busway; and

Figure 8 is a View similar to Figure 7, but showing the stationary power take-off device of Figure 5 in place on a power distribution duct or busway.

Referring to Figure 1, there is shown a power distribution duct or busway power take-off device of the trolley type incorporating the invention and comprising a carriage or main support 1, adapted to be supported in rolling engagement with rail surfaces R of a distribution duct D (Figure 7) by means of wheels 2 afiixed to axles 3, wheels 5 are also provided which are adapted to engage the under side of the duct D to restrict tipping.

An insulating carrier or casing, generally designated at 6, is afixed by suitable means such as by screws 4 to the support 1, and carries a pair of contact assemblies including contacts 7 adapted to slidably engage bus bars 28. Casing 6 includes two halves 9, 10 enclosing the contact assemblies 8. The two halves 9, 19 are joined by suitable fasteners such as by screws or rivets 11. An insulating cover member 12 is secured to the casing by suitable fasteners such as by screws or rivets 12a.

The casing 6 includes a depending portion 6a adapted to house conductors 13 which lead to a power consuming device (not shown). The halves 9, 1G or" the casing 6 are each formed with a recess 14 partially enclosed by a wall 15 terminating in a generally cylindrical enlargement 16 leaving a restricted passageway between the enlargement 16 and the wall 14 of the casing 6. A recess 17 is also provided in the meeting face of each casing half and arranged to communicate with the recess 14 of the opposite casing half when the casing 6 is assembled.

Each contact assembly includes a thermally responsive bimetallic member or strip 18, bent into a generally U- shaped form, with an arcuate bight portion 18a and opposed leg portions 18b, 180. The bimetallic strip 18 is arranged so that the side thereof having the greater coefficient of thermal expansion is inside the U, so that the U will expand and the free ends move away from each other upon increase in the temperature of the bimetallic strip, as shown by the double arrow in Figure 4. An offset or shoulder 19 is formed in leg 18b of the bimetallic strip 18, for cooperation with a compression spring member 20 which abuts leg 18b of the bimetallic strip when assembled in the contact structure. Shoulder 19 serves to prevent outward sliding of spring member 20 on the leg 18b toward the end thereof. A contact 7 is conductively affixed to leg of bimetallic strip 18 by suitable means such as by Welding. A flexible pigtail lead 21 is soldered or otherwise conductively affixed to bimetallic strip 18 at 22, and to a terminal 24, carried by the casing 6, at 23. Terminal 24 is provided with a threaded opening 25 receiving a terminal screw 26 to secure one of the conductors 13 thereto.

The contact assembly 8 is assembled in casing 6 by placing spring 20 loosely in recess 17, and disposing the arcuate portion 18a of bimetallic strip 18 about cylindrical enlargement 16, with leg 18c lying outside and. parallel to the casing and the leg 18b lying within recess 14. Bimetallic strip 18 is thus pivotally supported in the casing 6 by sliding engagement with cylindrical enlargement .16 and Wall 14'. The free end of spring member 20 is disposed to abut leg 18b of bimetallic strip 18 adjacent shoulder 19.

A recess 27 is also provided in each of the casing halves9. and to. receive flexible pigtail lead 21.

Compression spring members 20 are'provided, positioned in each recess 17, which bias bimetallic strips-18 and contacts 7 respectively :outwardly. into engagement with electric'currentsupply conductors or bus barsl28, about circular enlargements 16 as pivots.

Thebimetallic'strips l8 are/connected electrically in series with the contacts 7, a'circuitrbeing established from bus bars 28, to contacts 7, to bimetallic strips 18, to.:pigtailsleads 21, terminalstrips 24, and conductors 13.

Spring members Ztlareso dimensioned, and busbars 28so spaced that when no'currentis flowing in the circuit and bimetallic strips 18 are therefore subject to ambient atmospheric temperature only, the bias produced by himetallic strips 18 and spring members20 is sufiicient to maintain contacts 7 in engagement with bus-bars 28, and to suificiently compress spring members 20 to insure the maintenance of their proper alignment relative to bimetallic strips 18. Thus, when no;current is flowing in the circuit, the current collector may be moved along-the ra ls or duct on rollers 2- easily'and without causingsubstantial frictional Wear of the contacts.

when current is drawn, however, it heats bimetallic strips 18 and causes them to deflectas previously described so that their free ends move apart, thus increasing the pressure of the cumulative bias of bimetallic strips l8 and spring members 20 urging contacts 7 against the bus bars 28.

--In Figures 5-, 6 and 8, there is shown a-stationary't-ype power takeoff device embodying-the invention. This embodiment comprises a contact structure generally indicated at 29 in Figure 6. A bimetallic strip ormember 30 of L-shaped'form is provided, in'which'the metal strip having the greater co-eflicient of thermal expansion is placed on the outside of the L, so that distortion caused by thermal expansion will cause movement ofthe free end in the direction of the arrow in FigureS. nLeg 31 is provided with a threaded hole 32 cooperating with a screw 33 for connection to incoming leads 13-. --An-opening 34 is formed in the bimetallic strip for attaching the strip 30 to a wall of the casing 6' in recess 43 by suitable means such as a screw or rivet (not shown).

A contact 35 is secured to a contact bearing bracket 36, which is provided with flanges 37 and inwardly bent tongues 38. A compression spring member-39 is interposed between contact carrying element 36 andthe-free end 40 of bimetallic strip 30 as best seenin Figure- 6,

and is engaged by bent-up tongues 38 tosecure it at one end to element 36. A flexible pigtail lead 41 is soldered or otherwise conductively-aifixed to-' free end 40' of bimetallic strip 30 and to element 36. A' casing 6, comprising halves 9', 10 is provided for=mounting the contact assembly 29. Casing halves 9', 10' are each provided with suitable mating recesses .42, 43 and .opening 44. Opening 44 ismade of a"size to permit relative sliding motion of element36 therethrough but to" limit movement of element 36 outwardly out of "easing 6' by means of the engagement offianges 37 with'thet interior surface'of recess 42. 'Spring'member 391thus biases contact carrying bracket 36' outwardlyto urgethe conpus bars'45. The current collector may be "moved along the rails or duct on rollers 2 without incurring substantial frictional wear' of contacts 35 upon bus bars""45. When current is drawn, however, the strip deflects and increases the contact pressure.

It will be observed that although the invention is especially suited for use in applications where power is drawn only when the collector is stationary, it is also beneficial in any application where power is drawn-.in-yarying amounts or in= anintermit tent-fashion from a movable collector, since the contact pressure, and hence the wear on the contacts is reduced whenever the currentdrawn from the collector is reduced.

It 'should be understood that ,the, invention is. not limited to specific details of construction and arrange ment thereof herein illustrated, andthat changes and modifications may readily be made and I therefore intend. by the appended claims to cover all such changes and modifications asfallwithinthe true spirit andscope of my invention.

What I claim as new and desire to secure'by..Letters. Patentof the United States is:

1.- For use witha trolleyv type-power distribution system having an elongated housing and at least one conductor, carried by-said-housing, a. trolley type powertakei-ofi' device .comprisingvv a support,--means..for .mountingssaid' support to provide relative movement between. said sup-' port'and .the housing when .the.support is used in com-; bination therewith, at least one electrical contact member; movably supported on saidsupport and disposed and arranged to contact said=conductor .when said device is supported on said housing, .an elongated bimetallic striphaving a-firstt portion mounted onsaid supportand a second portion movable with. respect to. said support, means connecting saidcontact and said bimetallic strip electrically in series, and means connecting said second portion of; said bimetallic strip to said contactdn force-- transmitting-"relation, said bimetallic strip .being. constructed'to deflect when heated by current passing therethrough in a direction to exert a force on said .contact through said force-transmitting means.

2. A trolley type powertake-ofi device as set forthjn claim 1, said device also comprising a compressionspring having one end thereof in engagement with said bimetallic stripandhaving the other end thereof disposedand arranged so that said spring when compressedexertsa force upon said contact in thesame direction assaid I force exerted thereon by said bimetallic strip.

3. Foruse with .a trolley typesdistribution system having an, elongated housing and at least oneconductor carried by said housing, a trolley type powerMtake-ofi device comprising a support, means for mountingflsaid support to :provide relative movement between: said .support and the housing when the support .is used incombination therewith, at least one elongated generally ushapedybimetallic strip .member pivotally mounted. ,on said, support adjacent thebight of said U, an electrical :contact; mounted-on. one-end of saidxbimetallicstrip member and :adapted'to be moved thereby outwardly. of said support for: engagement with said .conductor when saiddevice is supported on said housing, a compression spring between the other end of ..said..bimetallic..st rip --member-and2-said support,.an electrical terminalmember mounted on said support, means connecting said ter minal member electrically to .said other-end of said bimetallic strip member, saidbimetallic strip member having itsphigh expansion side on theinside of said U whereby said bimetallic strip member deforms when heated by current flowing :therethrough in a direction to open said U and to increase the bias of said compression spring on'said contact. I

4; For use'with a trolley type power distributionsystem' having an elongated housing and' at least-one conductor carried by said housing, a trolley type power-take- "on devicecomprising a I support, roller means :mounted ing and permitting rolling movement of said device along said housing, at least one electrical contact member movably supported on said support and disposed and arranged to contact said conductor when said device is supported on said housing, an elongated bimetallic strip member having one end thereof movable with respect to said support, an electric terminal member mounted on said support and electrically connected to said first end of said bimetallic strip member, flexible electrical conductor means connecting said other end of said bimetallic strip to said contact member, and a compression spring having one end thereof in engagement with said contact member and having the other end thereof in engagement with said bimetallic strip member, said bimetallic strip 'member being constructed and arranged to deform when 15 2,740,942

heated by current passing therethrough so as to move said other end toward said compression spring to transmit contact pressure therethrough to said contact, member.

References Cited in the file of this patent UNITED STATES PATENTS 1,943,958 Grant Ian. 16, 1934 2,077,587 Rowe Apr. 20, 1937 2,128,135 Glasgow Aug. 23, 1938 2,170,298 Frank Aug. 22, 1939 2,361,536 Frank Oct. 31, 1944 2,537,866 Tanner Ian. 9, 1951 Sprigg Apr. 3, 1956 

